Wireless telemetry systems use a wireless (e.g., radio frequency) communications network to allow the measurement of information by remote devices and the transmission of the measured information to a central monitoring station (CMS). Typical wireless telemetry systems also enable the control of a remote device through the counter part of telemetry, telecommand.
In general, telemetry systems are employed for the purpose of monitoring environmental conditions or equipment parameters. Such systems are employed in a wide variety of applications including security, health monitoring, vehicle and asset tracking, and device and equipment monitoring and control.
A typical telemetry system includes a number of remote measuring devices, an encoder for encoding the measurements as analog or digital communication signals, and a transmission means for transmitting the communication signals.
For many telemetry applications it is critical that information obtained by the remote devices be transmitted to the monitoring system quickly. For example, if security alarm information or health status information is not transmitted quickly it may be not only useless, but detrimental as well. Therefore, for a telemetry system to be effective, it should be able to communicate data between remote devices and the monitoring station quickly.
Some telemetry systems use a wireless telecommunications system to transmit the telemetry application data. If the traffic channel of the system is used for data transmission, it can result in undesirable delay. That is, the delay associated with setting up a call to transmit the telemetry application data may be excessive for some applications.
This problem has been addressed in the context of the communication systems using the Advanced Mobile Phone Service (AMPS) standard. U.S. Pat. No. 5,845,203 to Ladue ('203 patent) describes a method for communicating ASD (e.g., telemetry application data) over a control channel of a wireless communication network. ASD from a remote device is encoded in a stream of dialed digits along with a remote feature control request (RFCR).
The RFCR function provided in AMPS allows a roaming cell phone to invoke a feature (e.g., speed dialing) from a home location register (HLR) associated with the local (home) Mobile Switching Center (MSC) to which the cell phone is assigned.
The RFCR is placed in the dialed digits stream accompanying a call origination message initiated by the roaming cell phone. The serving MSC in the visiting cellular service area, upon receiving the call origination message and detecting the RFCR in the accompanying dialed digits stream, forwards the RFCR over a nationwide cellular radio telecommunications intersystem network (e.g., a signaling system 7 (SS7) network), to the HLR associated with the roaming cell phone's home MSC.
The system described in the '203 patent exploits the RFCR to transmit ASD from the remote device to the CMS. The remote device is assigned a Mobile Identification Number (MIN) so that it appears as a roaming cell phone to a local MSC. The local MSC then, acts as the serving MSC for remote device. The area code specified in the assigned MIN is selected so that the CMS functions as the HLR associated with the home MSC for the remote device. The CMS further appears as a service control point (SCP) on the SS7 network to receive the RFCR and ASD automatically forwarded by the serving MSC.
This is effected as follows. An RFCR is placed in the dialed digits stream accompanying a call origination message initiated by the wireless communicator. Additionally, ASD is also placed in the dialed digits stream. The call origination message and dialed digits stream is transmitted over a control channel to the serving MSC. The serving MSC receives the call origination message and associated dialed digits stream, and detects the RFCR, triggering the serving MSC to forward the dialed digits stream, including the RFCR and the application-specific data, over the SS7 network, to the CMS/SCP.
This scheme provides several advantages including widespread geographic and infrastructure applicability, no need to access the traffic channel (low cost), no need to modify the serving MSC hardware or software.
However, the scheme is not without disadvantages and a significant one is that it is limited to communication systems employing standards that provide the specific “feature access request” function (i.e., AMPS). Moreover, the interpretation of feature requests may vary from carrier to carrier. For example, “*74” may be interpreted to signify a call-forwarding message by a particular carrier, but such interpretation is not specified by the standard and therefore a different carrier may have a different interpretation.
One widely-used digital wireless communications standard that does not provide the AMPS feature access request functionality is GSM. One method of transmitting the ASD in GSM communication networks is via the short message system (SMS). This method is disadvantageous in that the message is transmitted over the network traffic channel. Such methods are costly and slow as they invoke airtime charges and they require call setup prior to transmission of the message as well as call teardown afterwards.
What is needed is a method for transmitting ASD over a control channel of a GSM communications network.